Hydrogenation catalyst, a process for its preparation and use thereof

ABSTRACT

A process for hydrogenation of an aldehyde selected from the group consisting of propanal, n-butanal, and i-butanal comprising contacting said aldehyde with hydrogen in the presence of a hydrogenation catalyst comprising in the reduced state 
     25% to 50% by weight of metallic nickel 
     10% to 35% by weight of nickel oxide 
     4% to 12% by weight of magnesium oxide 
     1% to 5% by weight of sodium oxide 
     the remainder being a water insoluble support material, wherein the total of said nickel and said nickel oxide is 40% to 70% by weight based on said catalyst, said catalyst having a total BET surface area of 80 to 200 m 2  /g and a total pore volume, determined by mercury porosimetry, of 0,35 to 0.6 ml/g, 
     said total volume consisting of 30% to 60% of said volume from pores having pore radii equal to or less than 40 Å, 4% to 10% of said volume from pores having pore radii from more than 40 Å to 300 Å, and 30% to 60% of said volume from pores having pore radii from more than 300 Å to 5000 Å.

This application is a division of application Ser. No. 08/217/151 filedMar. 24, 1994, now U.S. Pat. No. 5,498,587.

This Application claims the benefit of the priority of GermanApplication P 43 10 053.8, filed March 27, 1993.

The present invention relates to a reduced hydrogenation catalystcomprising nickel, nickel oxide, magnesium oxide, and a water-insolublesupport material, a method of its preparation and the preferred usethereof in the hydrogenation of certain aldehydes.

BACKGROUND OF THE INVENTION

Catalysts based on nickel as the active catalyst component for thehydrogenation of aldehydes are part of the prior art. For example,EP-A-322 049 describes a hydrogenation catalyst comprising

1) a molar ratio of SiO₂ /Ni=0.15-0.35

2) a molar ratio of (Mg or Ba)/Ni=0-0.15,

in which part of the nickel is present in metallic form.

The known hydrogenation catalysts based on nickel can be used in thehydrogenation of aldehydes only at temperatures up to about 100° C.,since increasing the hydrogenation temperature leads to the formation ofundesired by-products which can sometimes only be removed by complicateddistillation.

SUMMARY OF THE INVENTION

It was, therefore, an object of the invention to provide a hydrogenationcatalyst which has high selectivity and produces conversions of over99.5% with high throughput rates at hydrogenation temperatures above110° C.

This object is surprisingly achieved by means of a hydrogenationcatalyst containing

25% to 50% by weight of (metallic) nickel

10% to 35% by weight of nickel oxide

4% to 12% by weight of magnesium oxide

1% to 5% by weight of sodium oxide

The reminder is support material.

The total of nickel and nickel oxide is from 40% to 70% by weight, thesurface area (determined by BET) is 80 to 200 m₂ /g, and the total porevolume (determined by Hg porosimetry) is 0.35 to 0.6 ml/g. The totalpore volume is made up of 30% to 60% by volume of pores having poreradii ≦40 Å, 4% to 10% by volume of pores having pore radii of more than40 and up to 300 Å, and 30% to 60% by volume of pores having pore radiiof more than 300 and up to 5000 Å.

The hydrogenation catalyst of the invention preferably has the followingfurther characteristics:

a) 5 to 10 atomic layers on the surface of the hydrogenation catalystcontain, as determined by SAM analysis, 18 to 30, preferably 20 to 28,atom % Ni, 1.2 to 3.0, preferably .5 to 2.5, atom % Na, and 2.8 to 4.8,preferably 3.2 to 4.5, atom % Mg;

b) the metallic nickel surface area is, as determined by chemisorptionof hydrogen, 100 to 130 m^(2/) g Ni;

c) the catalyst contains aluminium oxide or silicon dioxide,particularly in the form of silicic acid, silica gel, kieselguhr, orsiliceous earth, as the support material.

The invention further relates to a process for producing thehydrogenation catalyst, which comprises preparing, in a precipitationstep, a green catalyst from a nickel salt, a magnesium salt, sodiumcarbonate, and the support material, separating off the mother liquorand partially washing the precipitate, slurrying the green catalyst inalkali solution, separating it from the liquid phase, drying it, andcontacting the dried green catalyst with hydrogen until 42% to 83% byweight of the total nickel content is present in metallic form.

In a preferred form of the process, an aqueous solution, at 95° to 100°C., containing 0.5 to 0.8 mols/liter of a nickel salt and 0.1 to 0.2mols/liter of a magnesium salt, is stirred into a 0.9 to 1.1 molarsodium carbonate solution, also at 95° to 100° C., until the molar ratioof Na₂ CO₃ /(Ni+Mg) is 1:0.60 to 0.65. The support material isimmediately added over a period of 0.5 to 5 minutes and the greencatalyst formed is filtered off from the mother liquor and partiallywashed with hot water until the effluent wash water has a conductivityfrom 1500 to 2000 μS. The green catalyst is then suspended in 1 to 3times its volume of water and either 0.06 to 0.08 mol of sodiumhydroxide solution or 0.03 to 0.04 mol of sodium carbonate per mol ofnickel used in the precipitation step is stirred in. After stirring for1 to 5 hours at 40° to 60° C., the green catalyst is separated off fromthe suspension.

After drying, the green catalyst which has been separated off from thesuspension is reduced at 350° to 450° C. by treatment with 0.5 to 5.0standard m³ /hour of reduction gas per kilogram of green catalyst; thereduction gas contains 80% to 100% by volume of hydrogen. Mostpreferably, 1 to 3 standard m³ /hour of reduction gas is used perkilogram of the dried green catalyst. For better shaping, 0.5% to 5% byweight of graphite may be added to the hydrogenation catalyst.

The hydrogenation catalyst of the invention is particularly useful forthe hydrogenation of propanal, n-butanal, and i-butanal, preferably at110° to 160° C. This reaction can be carried out with simultaneousgeneration of steam under pressure to improve the economics of theprocess. In comparison with conventional hydrogenation catalysts, thehydrogenation can be carried out at increased catalyst loads of 0.8 to1.0 kilograms/hour of aldehyde per kilogram of catalyst. The selectivityis greater than 99.5%, usually greater than 99.9%; about 0.01% of thealdehyde used remains in the final product.. Less than 0.1% of thealdehyde is converted into carbon monoxide, ethers, acetals, and esters.Moreover in the hydrogenation of n-butanal, the formation of dibutylether less than 50 ppm, allowing distillation of the final product to beomitted. In the hydrogenation of n-propanal, the formation of dipropylether is less than 20 ppm.

The analytical methods employed are as follows:

1. BET determination of surface area

The method for determining the BET total surface area according toBrunauer, Emmett and Teller is described in J. Amer. Chem. Soc. 60(1938), page 309.

2. Determination of pore volume by Hg porosimetry (total pore volume andpore distribution)

The method for the determination of pore volume by Hg porosimetry up to3900 bar is according to H. L. Ritter, L. C. Drake and is described inInd. Engng. chem. analyt. Edit, 17 (1945) 782.

3. Determination of surface area by chemisorption

The method for determining the surface area of the nickel bychemisorption, viz. the amount of hydrogen absorbed at 20° C., isdescribed in J. of Catalysis 81 (1983) 204 and 96 (1985) 517.

4. Determination of pore radius

The method for the determination of pore radius is described by S. J.Gregg, K. S. W. Sing, Adsorption Surface Area and Porosity, AcademicPress New York-London (1967), pages 160 to 182.

5. Surface analysis by SAM spectroscopy (Scanning Auger Microprobe)

The analyses were carried out with a SAM spectrometer model PHI 660 fromPerkin-Elmer.

The chamber, into which the samples are placed, is evacuated to ≦1×10⁻⁸torr by a turbomolecular pump. An electron gun produces an electron beamwhich is fired at the sample. Because of strong charging of the samplesby the stream of electrons, MULTIPLEX measurements are carried out at 5different points on each sample; however, only the energy ranges of theelements to be expected are scanned, so as to minimize the measurementtime as much as possible.

The measurement and analysis of the AUGER electrons emitted from thesample is carried out by means of a cylindrical mirror analyzer. Thefollowing conditions were selected in the analyses:

    ______________________________________                                        Energy resolution (E/E):                                                                            0.6%                                                    Activation energy:    10 kV/10 mA                                             Lateral resolution:   about 220 nm                                            ______________________________________                                    

The quantitative evaluation was based on the sensitivity factors of thepure elements, which are published in the "Handbook of AugerSpectroscopy". The corresponding values for the elements nickel, sodiumand magnesium were measured and evaluated. The SAM analysis method isdescribed in detail in "Practical Surface Analysis by Auger and X-rayphotoelectronic Spectroscopy" by D. Briggs and M. Seah, John Wiley andSons, New York, London (1983), pages 217 ff. and 283 ff.

Properties of the hydrogenation catalyst

The specific physical and chemical properties of the hydrogenationcatalyst, which in the final analysis are the prerequisites for itsadvantageous hydrogenation behavior, are desirably achieved by thefollowing features and measures in its preparation.

In the precipitation step, the mixed basic nickel-magnesium carbonateand the deposition thereof on the support material should be carried outjointly. The precipitation conditions are selected so that theproportion of the precipitate comprising basic magnesium carbonate ispresent in as sparingly soluble a form as possible. The green catalystobtained in the precipitation step is, according to the invention, onlypartially washed so that little precipitated basic magnesium carbonateis washed cut of the green catalyst. The invention includes thecontrolled subsequent alkalization of the partially washed greencatalyst, whereby the required enrichment of the catalyst surface withalkali is achieved. The drying of the green catalyst is not critical. Itcan be carried out within a relatively broad range of drying conditions,for example in a stream of air at from 50° to 100° C.

A critical feature of the present invention is the relative percentagesof metallic nickel and nickel oxide in the reduced catalyst. This can beachieved by reducing the green catalyst using hydrogen. This reductionis to be carried out in such a way that the temperature of 350° to 450°C. and the hydrogen flow rate of 0.25 to 0.75 m/second results in only apartial reduction of the nickel-containing component. A degree ofreduction from 48% to 86% has proven to be advantageous.

When used in fixed-bed hydrogenation, the green catalyst is shaped priorto drying, for example into an extrudate, dried, reduced, and used inthis form or stabilized after reduction by treatment with small amountsof oxygen in nitrogen in a known manner (H. Blume, W. Naundorf and A.Wrubel, Chem. Techn., volume 15 (1963), page 583).

It has been found that sodium depletion at the surface of thehydrogenation catalyst causes an increase in cleavage and secondaryreactions which leads to loss of valuable products. Excessive sodiumconcentrations at the surface of the hydrogenation catalyst results inan increasing decline in the hydrogenation activity. In addition, thereis a tendency to form aldolization products. The sodium content in thesurface layer is required in the hydrogenation catalyst for controllingthe selectivity and thus for suppressing cleavage and secondaryreactions. The increased sodium concentration in the surface layer isachieved by slurrying the green catalyst in an alkali solution.

Magnesium depletion at the surface of the hydrogenation catalystengenders an altered pore structure which is unfavorable compared withthe catalyst of the invention. It also provides an increase in thecatalyst activity which leads, particularly in the hydrogenationtemperature range above 100° C., to the formation of undesiredby-products , especially cleavage products; a large magnesium excesscauses inactivation and thus lowers the performance of the hydrogenationcatalyst.

The examples below serve to illustrate the present invention withoutlimiting it.

PREPARATION EXAMPLE

Preparation of the hydrogenation catalyst

1906 g of Ni(NO₃)₂.6H₂ O and 355.6 g of Mg(NO₃)₂.6H₂ O are dissolved in10.4 liters of water at 99° C. 1500 g of anhydrous Na₂ CO₃ are dissolvedin 14 liter of water at 99° C. in a reactor equipped with a stirrer.While stirring vigorously, the Ni-Mg solution is then introduced at auniform rate into the sodium carbonate solution over a period of 3minutes. 230 g of kieselguhr is added in powder form and the suspensionformed is stirred for a further 3 minutes and subsequently filtered. Thefilter cake is washed with 27 liters of water at a temperature of 70° C.The last wash water running off has a conductivity of 1800 μS.

The filter cake is suspended in 6000 g of a 0.25% by weight sodiumhydroxide solution, stirred for 2 hours at 50° C., and filtered on afilter press. The filter cake formed is treated with compressed air for1 minute. The filter cake contains 82% water; in this form, the filtercake is formed into pellets (6 mm diameter). The shaped filter cake isdried in a drying chamber for 5 hours at 50° C., 3 hours at 60° C., andfor 8 hours at 75° C. to a constant weight.

The green catalyst had the following analysis:

    ______________________________________                                        Ni                  37.8% by weight                                           MgO                  5.2% by weight                                           Na.sub.2 O           1.1% by weight                                           CO.sub.2             6.0% by weight                                           Support material    22.7% by weight                                           Moisture             6.5% by weight                                           Bulk density        530 g/l                                                   ______________________________________                                    

The green catalyst is reduced at 425° C. over a period of 4 hours. Forthis purpose, 6 standard m³ /hour of reduction gas are passed over 2kilograms of green pelletized catalyst. The reduction gas comprises99.5% by volume of hydrogen and 0.5% by volume of nitrogen. A weightloss of 0.76 kilograms is observed on reduction. For a total nickelcontent of 53% by weight, a degree of reduction of 72% is determined inthe reduced catalyst.

Application Example 1

Hydrogenation of n-butanal

The catalyst prepared according to the Preparation Example, in the formof 6 mm pellets (250 ml), is first brought to 120° C. at a heating rateof 20° C./hour in a stream of hydrogen of 730 standard liters/hour at 4bar in a tube reactor provided with a heating/cooling jacket (internaldiameter: 32 mm). After reaching 120° C., 50 ml/hour of n-butanal(liquid) is fed into the vaporizer which is upstream of the reactor andthrough which 730 standard liters/hour of H₂ flow, at a vaporizertemperature of 100° C.. The H₂ /butanal-vapor mixture is heated to thereactor temperature in a preheater which is also upstream of thereactor. After 12 hours, the n-butanal feed rate is increased to 75ml/hour and, after a further 12 hours, is increased to 100 ml/hour.Thereafter, the butanal feed is increased in steps of 25 ml/hour atintervals of 24 hours. During the increase in the butanal feed, thepreheater reactor temperatures are simultaneously increased as follows:

    ______________________________________                                                                Preheater/reactor                                     n-Butanal feed                                                                              Time      temperature                                           (ml/h)        (h)       (°C.)                                          ______________________________________                                        200           24        123                                                   225           24        126                                                   250           continuous                                                                              128                                                                 operation                                                       ______________________________________                                    

The amount of H₂ is kept constant during the feed increase period andduring the continuous operation.

The hydrogenation product obtained in vapor form is condensed andanalyzed. It comprises 99.9% by weight of n-butanol and contains lessthan 0.1% by weight of unconverted n-butanal as well as <20 ppm ofdi-n-butyl ether as an unwanted by-product. In addition to thehydrogenated product, about 0.4 kg of steam per kg of n-butanal used isobtained at >1.8 bar during continuous operation (the steam pressurecorresponds to the reactor temperature).

APPLICATION EXAMPLE 2

Hydrogenation of propanal

The catalyst prepared according to the Preparation Example, in the formof 6 mm pellets (250 ml), is first heated to 125° C. at a heating rateof 20° C./hour in a stream of hydrogen (730 standard liter/hour) at 3.5bar in the reactor system described in Application Example 1. Liquidpropanal is then fed into the vaporizer at an initial rate of 50 ml/hourfor a period of 12 hours. The propanal feed rate is increased atintervals of 12 hours by 25 ml/hour each time up to 150 ml/hour. Onreaching the feed rate of 150 ml/hour, the preheater and reactortemperatures are increased to from 128° to 130° C.

The hydrogenation product obtained is condensed by cooling and analyzed.It comprises about 99.9% by weight of n-propanol and less than 0.1% byweight of unconverted propanal. By-products determined are less than 100ppm of 2-methylpentan-3-one and less than 20 ppm of di-n-propyl ether.As in Application Example 1, it is also possible to obtain steam (≧1.3bar) in the hydrogenation of propanal with the catalyst of theinvention.

APPLICATION EXAMPLE 3

Hydrogenation of i-butanal

For the hydrogenation of i-butanal, the catalyst (250 ml) of thePreparation Example is heated to 120° C. under hydrogen under the sameconditions as in Application Example 1. Subsequently, 50 ml/hour ofi-butanal is introduced. Hydrogenation pressure (3.5 bar), reactortemperature (120° C.), and H₂ feed rate (730 standard liters/hour) arekept constant. The resulting hydrogenation product comprises ≧99.95% byweight of i-butanol and contains ≦0.03% by weight of unconvertedi-butanal and less than 20 ppm of di-i-butyl ether. The hydrogenation ofi-butanal on the catalyst of the invention generated steam at ≧1.8 bar.

COMPARATIVE EXAMPLE

Hydrogenation of n-butanal

In the same tube reactor described in Application Example 1, 250 ml ofthe commercial nickel catalyst 55/5TST (HOECHST AG) in the form of 6 mmpellets is heated to 100° C. at a heating rate of 20° C./hour in astream of hydrogen of 730 standard liter/hour at 3.5 bar. 50 ml/hour ofliquid n-butanal is then fed into the vaporizer upstream of the reactor,the vaporizer being at 100° C. and having 730 standard liters/hour ofhydrogen flowing therethrough. Prior to entering the reactor, thehydrogen butanal vapor mixture is heated to the reactor temperature in apreheater. After 12 hours, the feed rate of n-butanal is increased to 75ml/hour and is increased at intervals of 12 hours up to 150 ml/hour.

These reaction conditions result in a hydrogenation product whichcontains 98.9% by weight of n-butanol, 0.3% by weight of acetals, 0.3%by weight of trimeric aldolization products of the butanal, 0.1% byweight of hydrocarbons, 0. 1% by weight of 2-ethylhexanol, 0.1% byweight of di-n-butyl ether, and from 200 to 300 ppm of butyric acidbutyl ester. Of the n-butanal used, from 1.0 to 1.2% by weight areconverted via hydrogenolysis into propane and methane which arecontained in the outflowing hydrogen stream.

In contrast to the catalyst of the invention, use of the commercialcatalyst gives considerable amounts of unwanted by-products, even at100° C. A particular difficulty in the isolation of pure n-butanol isthe distillative removal of the di-n-butyl ether which, with increasingester contents, leads to disproportionate losses of n-butanol. A furtherdisadvantage, compared to the catalyst of the invention, is therelatively high loss of the desired product (more than 1% by weight)caused by hydrogenolysis.

If the feed of n-butanal is increased to above 150 ml/hour, there is anincrease in the formation of di-n-butyl ether and cleavage products as aresult of hydrogenolysis. The same effects occur on raising thehydrogenation temperature. In comparison with the catalyst of theinvention, the catalyst of the prior art enables a maximum conversion ofonly 60% of the amount of aldehyde, with the hydrogenation productsobtained also being more contaminated. A further disadvantage is thelimiting of hydrogenation temperature to a maximum of 100° C., at whichno usable steam can be obtained.

While only a limited number of specific embodiments of the presentinvention have been expressly disclosed, it is, nonetheless, to bebroadly construed, and not to be limited except by the character of theclaims appended hereto.

What we claim is:
 1. A process for hydrogenation of an aldehyde selectedfrom the group consisting of propanal, n-butanal, and i-butanalcomprising contacting said aldehyde with hydrogen in the presence of ahydrogenation catalyst consisting essentially of in the reduced state25%to 50% by weight of metallic nickel 10% to 35% by weight of nickel oxide4% to 12% by weight of magnesium oxide 1% to 5% by weight of sodiumoxidethe remainder being a water insoluble support material, wherein thetotal of said nickel and said nickel oxide is 40% to 70% by weight basedon said catalyst, said catalyst having a total BET surface area of 80 to200 m₂ /g and a total pore volume, determined by mercury porosimetry, of0.35 to 0.6 ml/g, said total volume consisting of 30% to 60% of saidvolume from pores having pore radii equal to or less than 40 Å, 4% to10% of said volume from pores having pore radii from more than 40 Å to300 Å, and 30% to 60% of said volume from pores having pore radii frommore than 300 Å to 5000 Å.
 2. The process of claim 1 wherein saidhydrogenation is carried out at 100° to 160° C.